The overall objective of this proposal is to elucidate the mechanism by which hormones regulate growth and differentiated function in the normal mammary gland, and how these regulatory mechanisms have deviated in hormone-dependent mammary cancer. Specific emphasis is placed upon the mechanism by which prolactin regulates milk protein gene expression, as a model system for understanding peptide hormone action in general. In addition, the mechanism by which the steroid hormone, hydrocortisone, potentiates the action of prolactin is under investigation. Mammary gland organ culture employing a chemically-defined medium is being utilized to study the interaction of these hormones. Structural gene (mRNA-derived) DNA clones of the four rat milk protein genes are being utilized to study the synthesis, processing and turnover of the individual milk protein mRNAs. Distinct high molecular weight precursors for each of these mRNAs have been identified with the largest-sized transcript being greater than 5Kb. The organization of these genes is being studied using total DNA mapping and by screening a rat DNA library for the presence of these genes. Several positive plaques have been identified and the characterization of these genomic clones is in progress. The chromosomal localization of these genes is also being studied using somatic cell hybrids between CHO and mouse L cells. The mouse casein genes have been localized to a subset of mouse chromosomes and the homologous cloned mouse casein genes are now being used to perform fine mapping studies. The expression of the milk protein genes in hormone-dependent, DMBA-induced rat mammary carcinomas was only 1-2.5% of that observed in the normal gland under the same hormonal environment. This loss of differentiated function appears to occur in the majority of the tumor cell population (greater than 95%). Using molecular hybridization and cell-free translation the poly(A) plus and poly(A) minus RNA populations in the tumors and normal gland have been compared. No unique tumor-specific sequences were identified and the primary differences appeared to be in the different abundancies of certain RNAs, especially the milk protein mRNAs.